FinFET device with fins of non-uniform width

ABSTRACT

A fin-type field-effect transistor (FinFET) device includes a plurality of fins formed over a substrate. The semiconductor device further includes a dielectric layer filled in a space between each fin and over a first portion of the plurality of fins and a dielectric trench formed in the dielectric layer. The dielectric trench has a vertical profile. The semiconductor device further includes a second portion of the plurality of fins recessed and exposed in the dielectric trench. The second portion of the plurality of fins have a rounded-convex-shape top profile.

PRIORITY DATA

The present application is a continuation application of U.S. patent application Ser. No. 15/817,648, filed Nov. 20, 2017, which is a continuation application of U.S. patent application Ser. No. 14/882,144, filed Oct. 13, 2015, which is a divisional application of U.S. patent application Ser. No. 14/162,598, filed Jan. 23, 2014, each of which is incorporated herein by reference in its entirety.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experienced exponential growth. Technological advances in IC materials and design have produced generations of ICs where each generation has smaller and more complex circuits than the previous generation. In the course of IC evolution, functional density (i.e., the number of interconnected devices per chip area) has generally increased while geometry size (i.e., the smallest component (or line) that can be created using a fabrication process) has decreased. This scaling down process generally provides benefits by increasing production efficiency and lowering associated costs.

Such scaling down has also increased the complexity of processing and manufacturing ICs and, for these advances to be realized, similar developments in IC processing and manufacturing are needed. For example, a three dimensional transistor, such as a fin-type field-effect transistor (FinFET), has been introduced to replace a planar transistor. Although existing FinFET devices and methods of fabricating FinFET devices have been generally adequate for their intended purposes, they have not been entirely satisfactory in all respects. It is desired to have improvements in this area.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIG. 1 is a flow chart of an example method for fabricating a FinFET device in accordance with some embodiments.

FIG. 2 is a cross-section view of an example FinFET device precursor at fabricated stages constructed according to the method of FIG. 1.

FIGS. 3 to 9 are cross-sectional views of an example FinFET device at fabrication stages constructed according to the method of FIG. 1.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, or examples, for implementing different features of the invention. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.

The present disclosure is directed to, but not otherwise limited to, a FinFET device. The FinFET device, for example, may be a complementary metal-oxide-semiconductor (CMOS) device comprising a P-type metal-oxide-semiconductor (PMOS) FinFET device and an N-type metal-oxide-semiconductor (NMOS) FinFET device. The following disclosure will continue with a FinFET example to illustrate various embodiments of the present invention. It is understood, however, that the application should not be limited to a particular type of device, except as specifically claimed.

FIG. 1 is a flowchart of a method 100 for fabricating a FinFET device 500 according to aspects of the present disclosure. FIG. 2 is a cross-section view of a FinFET device precursor 200 at fabrication stages constructed according to the method 100 of FIG. 1. FIGS. 3-9 are cross-section views of the FinFET device 500 at fabrication stages constructed according to the method 100 of FIG. 1. The FinFET device precursor 200 and the FinFET device 500 are collectively described with reference to FIGS. 1-9. It is understood that additional steps can be provided before, during, and after the method 100, and some of the steps described can be replaced or eliminated for other embodiments of the method.

Referring to FIGS. 1 and 2, the method 100 begins at step 102 by receiving a FinFET device precursor 200. The FinFET device precursor 200 includes a substrate 210. The substrate 210 includes silicon. In another embodiment, the substrate may include germanium, silicon germanium, gallium arsenide or other appropriate semiconductor materials. Alternatively and for some embodiments, the substrate 210 may include an epitaxial layer. For example, the substrate 210 may have an epitaxial layer overlying a bulk semiconductor. Further, the substrate 210 may be strained for performance enhancement. For example, the epitaxial layer may include a semiconductor material different from those of the bulk semiconductor such as a layer of silicon germanium overlying bulk silicon or a layer of silicon overlying a bulk silicon germanium formed by a process including selective epitaxial growth (SEG). Furthermore, the substrate 210 may include a semiconductor-on-insulator (SOI) structure such as a buried dielectric layer. Also alternatively, the substrate 210 may include a buried dielectric layer such as a buried oxide (BOX) layer, such as that formed by a method referred to as separation by implantation of oxygen (SIMOX) technology, wafer bonding, SEG, or other appropriate methods. In fact various embodiments may include any of a variety of substrate structures and materials.

The FinFET device precursor 200 also includes a plurality of fins 220 and substrate trenches 230 (a space between each of fins) formed over the substrate 210. The fins 220 and the substrate trenches 230 may be formed by one or more procedures such as deposition, lithography and etching. In one embodiment, a first hard mask layer is formed over the substrate 210. The first patterned hard mask layer 215 may include may include silicon nitride, silicon oxide, silicon carbide, titanium oxide, titanium nitride, tantalum oxide, tantalum nitride, or any suitable materials. A patterned photoresist layer is then formed over the first hard mask layer to define fins 220 and the substrate trenches 230. Generally, a patterning process may include photoresist coating (e.g., spin-on coating), exposing, developing the photoresist, other suitable processes, or combinations thereof. Alternatively, the photolithography exposing process is implemented or replaced by other proper methods such as maskless photolithography, electron-beam writing, direct-writing, and/or ion-beam writing. The first hard mask layer is then etched through the pattern photoresist layer to form the first patterned hard mask layer 215. The substrate 210 is then etched through the first patterned hard mask layer 215 to form fins 220 and substrate trenches 230. The substrate 210 may be etched by various methods, including a dry etch, a wet etch, or a combination of thereof.

The FinFET device precursor 200 also includes a dielectric layer 240 formed over the substrate 210, including filling in the substrate trenches 230. In one embodiment, the substrate trench 230 filled with the dielectric layer 240 serves as an isolation region to separate various device regions in the substrate 210. The dielectric layer 240 may include silicon oxide, silicon nitride, oxynitride, a dielectric material having a dielectric constant (k) lower than thermal silicon oxide (therefore referred to as low-k dielectric material layer), or other suitable dielectric material layer. The dielectric layer 240 may include a single layer or multiple layers. In the present embodiment, the dielectric layer 240 may include a material which is different from the first patterned hard mask layer 215 to achieve etching selectivity during a subsequent etch process. The dielectric layer 240 may be deposited by chemical vapor deposition (CVD), atomic layer deposition (ALD) or spin-on coating. Additionally, a chemical mechanical polishing (CMP) process may be performed to planarize top surfaces of the dielectric layer 240. In the present embodiment, a final thickness of the dielectric layer 240 is controlled such that it is above the fins 220 with a first height h₁. The first height h₁ is designed to be adequate for a later isotropic dielectric etch, which will be described later.

Referring to FIGS. 1 and 3, once the FinFET device precursor 200 is received, the method 100 proceeds to step 104 by forming a second patterned hard mask layer 310 over the dielectric layer 240. The second patterned hard mask layer 310 has openings 315. The openings 315 are formed such that they align to a respective subset of fins 220, now labeled with the reference number 220A. The fins not aligned with the mask layer openings are labeled with the reference number 220B. In one embodiment, the subset of fins 220A includes more than one fin. In one embodiment, an edge of the opening 315 is designed to align having a distance “d” away from the nearest fin 220B. The distance d is designed to be adequate such that the fin 220B is not adversely affected during a later anisotropic dielectric etch, which will be described later.

The second patterned hard mask layer 310 may include silicon nitride, silicon oxide, silicon carbide, titanium oxide, titanium nitride, tantalum oxide, tantalum nitride, or any suitable materials. In the present embodiment, the second patterned hard mask layer may include a material being different from the dielectric layer 240 to achieve etching selectivity during a subsequent etch process. In one embodiment, the second patterned hard mask layer 310 includes the same material as the first patterned hard mask layer 215 to obtain a process flexibility in the subsequent etch, which will be described later. The second patterned hard mask layer 310 may be formed by one or more procedures such as deposition, lithography and etching and deposition.

Referring to FIGS. 1 and 4, the method 100 proceeds to step 106 by performing an anisotropic dielectric etch by using the second patterned hard mask layer 310 as an etch mask. Through the opening 315, a portion of the dielectric layer 240 is removed to form a dielectric trench 410 and expose the subset of fins 220A, including first patterned hard mask 215. The dielectric trench 410 is formed with a substantially vertical profile, which ensures that the fin 220B are not adversely affected during the anisotropic dielectric etch. The dielectric trench 410 has a first width w₁. The anisotropic dielectric etch may include a plasma dry etching process using a fluorine-based chemistry, such as CF₄, SF₆, CH₂F₂, CHF₃, and/or C₂F₆. The anisotropic dielectric etch selectively removes the dielectric layer 240 but does not substantially etch the subset of fins 220A. (That is, the etch rate on the fins 220A is significantly lower than that of the dielectric layer 240.) Thus a top portion of the subset of fins 220A is exposed in the dielectric trench 410. With the vertical profile of the dielectric trench, the distance d provides extra insurance that the fin 220B is not impacted adversely during the anisotropic etch. Thus, etch process constrains are relaxed. In one embodiment, a depth of the anisotropic dielectric etch is controlled such that the portions of the first patterned hard mask 215 on the fins 220A are fully exposed.

Referring to FIGS. 1 and 5, the method 100 proceeds to step 108 by removing the portions of the first patterned hard mask 215 on the fins 220A and the second patterned hard mask layer 310. The first patterned hard mask layer 215 and the second hard mask layer 310 may be removed by a selective dry etch, a selective wet etch, or combination thereof. The etching selectively removes both the first patterned hard mask layer 215 and the second hard mask layer 310 but does not substantially etch the dielectric layer 240 and the subset of fins 220A. In one embodiment, the first patterned hard mask layer 215 and the second hard mask layer 310 are removed in a single etch process. In this embodiment, the first patterned hard mask layer 215 and the second patterned hard mask layer 310 can be formed of similar material, which provides process flexibility and improves the process window of the etch process.

The method 100 has two paths after step 108, identified by the suffix “A” and “B,” respectively. Both paths are separately discussed below.

Referring to FIGS. 1 and 6, the method 100 proceeds to step 110A by performing a selective isotropic dielectric etch without using an etch mask. The selective isotropic etch selectively etches the dielectric layer 240 but does not substantially etch the subset of fins 220A in the dielectric trench 410. The dielectric layer 240 is etched in both of vertical and horizontal directions such that the first width w₁ of the dielectric trench 410 is enlarged to a second width w₂ and the first height h₁ of the dielectric layer 240 above the fin 220 is reduced to a second height h₂, but it is still adequate to protect the fins 220, including the fins 220B, during the selective isotropic dielectric etch. Here the vertical direction is a direction along a height of the fin 220 and the horizontal direction is perpendicular to the vertical direction. The dielectric trench 410 becomes deeper during the selective isotropic dielectric etch as well. Thus, the enlarged dielectric trench 410 (with a wider width and a deeper depth) may leave more space to facilitate a full exposure of a top portion of the subset of fins 220A (to be recessed later), which may improve the recess process window. The selective isotropic dielectric etch may include a dry etch, a wet etch, or combination thereof. In one embodiment, the selective isotropic dielectric etch includes a plasma dry etching process using NF₃-containing gases.

Referring to FIGS. 1 and 7, the method 100 proceeds to step 112A by recessing a portion of the subset of fins 220A in the dielectric trench 410. The recess selectively etches the subset of fins 220A but does not substantially etch the dielectric layer 240. The recessing process may include a selective wet etch or a selective dry etch, or combination thereof. In one embodiment, a selective wet etching solution includes a tetramethylammonium hydroxide (TMAH), a HF/HNO₃/CH₃COOH solution, or other suitable solution. Dry etching process may include a biased plasma etching process that uses a chlorine-based chemistry, such as such as Cl₂, CHC₁₃, CCl₄, and/or BCl₃). In one embodiment, the recess is an isotropic etch by using gases of Cl₂ with NF₃ in a ratio of 40:1 and leave a top portion of the recessed subset of fins 220A with a rounded-convex-shape top profile 415.

Referring to FIGS. 1 and 8, alternatively, after completing the step 108, the method 100 proceeds to 110B (instead of 110A) by anisotropically recessing the subset of fins 220A to form a sub-dielectric-trench 420 in the dielectric trench 410. In one embodiment, without using an etch mask, the anisotropic fin etch selectively etches the subset of fins 220A but does not substantially etch the dielectric layer 240. Therefore, the dielectric layer 240 protects the fins 220, including the fin 220B as well during the anisotropic etch. In the present embodiment, the anisotropic fin etch mainly etches in a vertical direction and a depth of the anisotropic etch is controlled to achieve a predetermined recessing depth. The anisotropic fin etch may include a dry etching process using a chlorine-based chemistry, such as Cl₂, CHCl₃, CCl₄, and/or BCl₃). In one embodiment, the anisotropic fin etch is a dry etching by using Cl₂ with oxygen in a ratio of 5:1.

Referring to FIGS. 1 and 9, after completing step 110A, the method 100 proceeds to 112B by isotropically etching the recessed subset of fins 220A in the sub-dielectric-trench 420. During previous anisotropic fin etch in step 110A, a residual film of the subset of fins 220A may be left along a sidewall of the sub-dielectric-trench 420 (also referring as a horn structure), which may cause current leakage leading yield loss of the FinFET device. The isotropic fin etch may help to remove those residual films of the subset of fins 220A. The isotropic fin etch selectively etches the subset of fins 220A but does not substantially etch the dielectric layer 240. In one embodiment, the isotropic fin etch leaves a top portion of the recessed subset of fins 220A with a rounded-concave-shape top profile 425 in the sub-dielectric-trench 420. The isotropic fin etch may include a wet etch or a dry etch, or combination thereof. In one embodiment, the isotropic fin etch is wet etching solution includes a TMAH, a HF/HNO₃/CH₃COOH solution, or other suitable solution. In another embodiment, the isotropic fin etch is a dry etch by using gases of Cl₂ with NF₃ in a ratio of 40:1.

The FinFET device 500 may also undergo further CMOS or MOS technology processing to form various features and regions known in the art. For example, high-k/metal gate (HK/MG) stacks are formed over the substrate 210, including over (wrapping) a portion of the fins 220. For another example, source and drain (S/D) regions are formed on each side of the HK/MG stacks. S/D regions may be formed by recess, epitaxial growth, and implant techniques. Subsequent processing may also form various contacts/vias/lines and multilayers interconnect features (e.g., metal layers and interlayer dielectrics) on the substrate 210, configured to connect the various features or structures of the FinFET device 500. For example, a multilayer interconnection includes vertical interconnects, such as conventional vias or contacts, and horizontal interconnects, such as metal lines. The various interconnection features may implement various conductive materials including copper, tungsten, and/or silicide. In one example, a damascene and/or dual damascene process is used to form a copper related multilayer interconnection structure.

Additional steps can be provided before, during, and after the method 100, and some of the steps described can be replaced or eliminated for other embodiments of the method.

Based on the above, the present disclosure offers methods for fabricating a FinFET device. The method employs forming a vertical dielectric trench to expose a subset of fins and being followed by an isotropic dielectric etch to an enlarging the dielectric trench. This dual dielectric etch scheme reduces a risk of impacting adversely on the fin adjacent to the dielectric trench. The method also employs a dual fin etch scheme of an anisotropic etch followed by an isotropic etch. The method effectively eliminates fin film residual issue in fin recess process. The method demonstrates improvements of process window and process flexibility.

The present disclosure provides many different embodiments of fabricating a FinFET device that provide one or more improvements over the prior art. In one embodiment, a method for fabricating a FinFET device includes receiving a precursor. The precursor has a plurality of fins over a substrate and a dielectric layer filling in a space between each of fins and extending above the fins. The method also includes forming a patterned hard mask layer having an opening over the dielectric layer, etching the dielectric layer through the opening to form a trench with vertical profile. A subset of the fins is exposed in the trench. The method also includes performing an isotropic dielectric etch to enlarge the trench in a horizontal direction, which is perpendicular to the vertical profile of the trench. The method also includes performing an anisotropic etch to recess the subset of fins in the trench and performing an isotropic fin etch to etch the recessed subset of fins.

In yet another embodiment, a method for fabricating a FinFET device includes receiving a precursor. The precursor has a plurality of fins over a substrate and a dielectric layer filling in a space between each of fins and extending above the fins. The method also includes forming a patterned hard mask layer having an opening over the dielectric layer, etching the dielectric layer through the opening to form a trench with vertical profile. Therefore a subset of fins is exposed in the trench. The method also includes recessing the subset of fins to form a subset of dielectric trenches in the trench and performing an isotropic fin etch to etch the recessed subset of fins in the subset of dielectric trenches.

In another embodiment, a FinFET device includes a substrate, a plurality of fins formed over the substrate, a dielectric layer filled in a space between each of fins and extends above the fins. The FinFET device also includes a dielectric trench in the dielectric layer and a subset of recessed fins are exposed in the dielectric trench.

The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. A device comprising: a first fin structure extending from a top surface of a substrate to a first height, the first fin structure having a first width at a first interface with the top surface of the substrate and a second width away from the top surface of the substrate, the first width being different than the second width; a second fin structure extending from the top surface of the substrate to a second height that is different than the first height, the second fin structure having the first width at a second interface with the top surface of the substrate; and a dielectric layer disposed on the substrate and extending from the first fin to the second fin, wherein the dielectric layer has a third width at a third interface with the top surface of the substrate and a fourth width away from the top surface of the substrate, wherein the third width is smaller than the fourth width.
 2. The device of claim 1, wherein the second fin structure incudes a portion above the second interface with the substrate that has the second width.
 3. The device of claim 1, wherein the first fin structure and the second fin structure each have the second width at a same height about the substrate.
 4. The device of claim 1, wherein the first fin structure includes a first semiconductor material and the second fin structure includes a second semiconductor material, and wherein the second height is less than the first height.
 5. The device of claim 1, wherein the dielectric layer includes a non-planar top surface extending between the first fin structure and the second fin structure.
 6. The device of claim 1, wherein the dielectric layer interfaces with both the first fin structure and the second fin structure, and wherein the dielectric interfaces with the first fin structure at a greater height above the substrate than the second fin structure.
 7. The device of claim 1, wherein the second width of the first fin structure is measured along a horizontal axis that extends parallel to the top surface of the substrate from a first sidewall edge of the first fin structure to an opposing second sidewall edge of the first fin structure, and wherein the dielectric layer interfaces with the first sidewall edge and the second sidewall edge of the first fin structure.
 8. A device comprising: a first semiconductor fin structure disposed over a substrate, the first semiconductor fin structure having a first width at a first interface with a top surface of the substrate; a second semiconductor fin structure disposed over the substrate, the second semiconductor fin structure having the first width at a second interface with the top surface of the substrate; and a dielectric layer disposed over the substrate and extending from the first semiconductor fin structure to the second semiconductor fin structure, wherein the dielectric layer has a second width at a third interface with the top surface of the substrate and a third width away from the top surface of the substrate, wherein the second width is different than the third width.
 9. The device of claim 8, wherein the second width is smaller than the third width.
 10. The device of claim 8, wherein the second semiconductor fin structure is taller than the first semiconductor fin structure.
 11. The device of claim 8, wherein the first semiconductor fin structure and the second semiconductor fin structure have substantially similar heights.
 12. The device of claim 8, wherein the first semiconductor fin structure has a non-planar top surface.
 13. The device of claim 8, wherein the first semiconductor fin structure and the substrate are formed of the same material.
 14. The device of claim 8, further comprising a third semiconductor fin structure positioned on a first side of the first semiconductor structure and the second semiconductor fin structure positioned on a second side of the first semiconductor fin structure, and wherein the first semiconductor fin structure is shorter than both the second semiconductor fin structure and the third semiconductor fin structure.
 15. The device of claim 8, wherein the dielectric layer includes a non-planar top surface extending between the first semiconductor fin structure and the second semiconductor fin structure.
 16. A device comprising: a first semiconductor fin structure disposed over a substrate, the first semiconductor fin structure including a first portion, a second portion and a third portion, the first portion of the semiconductor fin structure having a first width at a first interface with a top surface of the substrate, the second portion of the semiconductor fin structure disposed over the first portion and having a second width that is different than the first width, the third portion of the semiconductor fin structure disposed over the first portion and having a third width that is different than the second width; a second semiconductor fin structure disposed over the substrate, the second semiconductor fin structure having the first width at a second interface with the top surface of the substrate; and a dielectric layer disposed over the substrate and extending from the first semiconductor fin structure to the second semiconductor fin structure, wherein the dielectric layer has a fourth width at a third interface with the top surface of the substrate and a fifth width away from the top surface of the substrate, wherein the fourth width is different than the fifth width.
 17. The device of claim 16, wherein the second portion of the semiconductor fin structure is disposed over and interfaced with the first portion and the third portion of the semiconductor fin structure is disposed over and interfaces with the second portion.
 18. The device of claim 17, wherein the first width is greater than the second width and the second width is greater than the third width.
 19. The device of claim 16, wherein the dielectric layer interfaces with the first, second and third portions of the first semiconductor fin structure.
 20. The device of claim 16, wherein the dielectric layer interfaces with the first and second portions of the first semiconductor fin structure while the third portion is free of the dielectric layer. 